The present invention relates to an arrangement for determining the rotational behavior of a wheel or any other rotating body
A particularly important case of application for arrangements of this type is the measurement of wheel rotational speeds as an input quantity for an automotive vehicle control system, for example, for an anti-lock system (ABS), for a traction slip control system (TCS), for a driving stability control system (DSC, ASMS), etc. Arrangements of this type are also appropriate to measure other rotational movements in mechanical engineering.
Arrangements and devices to determine the rotational speed of a vehicle wheel are known and customary on the market in many types of design. The measurement systems which basically include a measuring data emitter configured as a toothed wheel or an encoder, and a pick-up for measuring data may principally be designed as passive or active systems or sensors. Inductive sensors, i.e., passive measuring systems, have previously been preferred for technological and cost reasons. Yet active sensors are gaining in usage.
WO 95/17680 (P 7805) describes an active rotational speed sensor. In this publication, the measuring device basically includes an encoder rotating with the wheel, a magnetoresistive sensor element having a permanent magnet that is used as a biassing magnet, and a signal-processing circuit which is incorporated in an integrated circuit. The output signals of the sensor are delivered to a central evaluating circuit.
German patent application No. 44 34 180 (P 7748) discloses a circuit for evaluating the output signal of an active sensor. The output signal of the sensor is a binary current signal having a frequency which contains the information about the rotational movement. The active sensor is a controllable power source which delivers a load-independent current. By way of an associated evaluating circuit, the active sensor is connected to the vehicle battery and is supplied by it with electrical energy.
In an automotive vehicle control system with rotational speed sensors, the output signals of the individual active sensors are generally conducted by way of a two-core cable to a central evaluating circuit which is connected to the vehicle battery and supplies the electrical energy for the operation of the active sensors by way of the two-core cable. Also, proposals have been made to use a single-core cable and to replace the second core by current supply via the vehicle body (P 8693).
The general object of the present invention is to reduce the total expenditure entailed for the measurement and evaluation of the sensed information and, more particularly, to reduce the effort in wiring between the individual sensors and the evaluating circuit or, in other terms, to improve the use of the necessary wiring between the individual active sensors and the (central) evaluating circuit.
It has been found that this object can be achieved by including a sensor module which comprises the sensor element, the power source and a modulator which controls the power source as a function of the signals of the sensor element and of external signals supplied by an external signal source and introduced through an additional port, and which produces as an output signal of the control module a current signal, representative of the rotational behavior, with a superimposed status signal or additional signal.
Thus, the arrangement of the present invention permits a multiple use of the wiring between the active sensor and the evaluating circuit. A special system concept is made use of to this end, wherein the sensor module which comprises a sensor element and a controllable power source is equipped with a modulator which controls the power source supplying the load-independent current in response to an additional external signal and impinges or superimposes an additional signal on the output signal of the signal, or adds a status signal, and delivers it to the central evaluating circuit. Thus, there is multiple use of the wiring.
The evaluating circuit includes a decoder or an identification circuit which identifies and evaluates the status signal or additional signal.
In a preferred aspect of the present invention, the sensor module further has another circuit, that is, an observer, which is connected to the lines interconnecting the sensor module and the evaluating circuit. The observer receives by way of these lines data supplied by the evaluating circuit and controls or monitors, in dependence on these data, the acceptance or processing of the data introduced by way of the additional port. It is possible, for example, to configure the system so that the observer polls and considers the data introduced by way of the additional port only at defined times or under defined conditions.
In another preferred aspect of the present invention, the sensor element of the sensor module has several sensor units for scanning the encoder or measuring data emitter according to different criteria and/or for redundantly identifying measuring values. The last-mentioned case permits monitoring the proper functions, for example.
In still another aspect of the present invention, an external signal source is connected to the additional port of the sensor module and produces a signal derived from the rotational movement of the encoder or any other rotating measuring data emitter irrespective of the sensor elements. Still other status signals determined by sensor means may be introduced through the additional port of the sensor module and conducted to the evaluating circuit by way of the modulator and the signal lines. It may be favorable to condition or evaluate the status signals in the modulator prior to their transmission. These operations can be controlled by the observer.
Further features, advantages and possible applications of the present invention can be seen in the following description of further details of embodiments of the present invention making reference to the accompanying drawings.